I. Field of the Invention
The present invention is directed to intrauterine pressure and fetal heart rate sensors and pressure transducers, and, more particularly to intrauterine pressure and fetal heart rate sensors and pressure transducers which are nonintrusive to the fetus during labor.
II. Discussion of the Prior Art
Presently, intrauterine pressure and fetal heart rate are monitored with two separate sensors. The fetal ECG is used in some devices, including the present invention, to determine fetal heart rate. In presently used devices, the intrauterine pressure is transmitted from the uterus to the external transducer diaphragm via a liquid column contained in various sizes of tubings. Such a liquid column is in direct contact with the amniotic fluid at its distal receiving end or through side holes in the tubing. The setup for such a system requires careful debubbling of the pressure catheter and transducer dome. Further, such a system requires frequent manual flushings for short-term applications and continuous flushing for long-term applications. Flushing is needed in such systems in order to avoid fluid coagulation in the monitoring line since the frequent contraction pressures present during labor will force the uterine fluid into the pressure tubing. In known systems, the uterine fluid contains materials which may completely clot the tubing unless the tubing is flushed frequently. Furthermore, since the prior art pressure sensor works on a hydraulic head differential principle, it requires frequent repositioning of the external transducer each time the mother changes position.
Current devices for sensing fetal ECG use positive fixation means, e.g., harpoon tip, a spiral or corkscrew-type electrodes which usually are anchored or screwed into the scalp of the fetus or a suction cup device. In certain circumstances, the placement and removal of such electrodes may result in serious and even permanent injury to the fetus. Such devices are used because prior to the invention, it was the accepted belief in the medical community that positive contact with the fetus was necessary at all times to enable sensing of the fetal ECG. It has now been discovered that fetal ECG may be sensed with the present invention whether or not direct contact is established with the body of the fetus, as long as the sensor is placed within the uterus. The uterus itself provides a conductive environment sufficient to allow monitoring of the fetal ECG, from which the fetal heart rate is derived.
Disadvantages of known pressure and fetal heart rate monitoring and sensing devices include, among other factors, considerable time to set up continual monitoring and flushing of the devices, possible excessive amount of liquid administered to the patient, increased contamination possibilities, additional cost for flushing, trauma and possible injury to the fetus and/or the uterus, additional procedure time for electrode removal and spontaneous electrode release from the fetus requiring reinsertion.